1. Field of the Invention
This invention relates to the analysis and evaluation of the results of ultrasonic examinations by the pulse-echo method of solid objects having a plane or locally substantially plane surface. The correct location, interpretation and sizing of internal flaws in materials and welded joints are matters of the greatest importance for the safety and fitness for purpose of important structures and installations.
2. Background of the Prior Art
In the ultrasonic examination art, great efforts have been made to develop improved systems for the location and sizing of flaws in materials and welded joints, in particular systems producing easily readable images of internal flaws. In many systems this has been made possible through the use of digital computing means including electronic matrix memories for the storage of echo data which may then be analysed, displayed on video monitors as grey scale or colour images, and permanently recorded by magnetic recording means or permanent prints.
In a previous patent application, WO, Lund et al., 87/07026, we have disclosed a system for ultrasonic examination providing sectional and projection views showing flaw images of greatly improved precision and sharpness of definition.
According to said previous invention, at least one ultrasonic probe is moved over the surface of the object examined in steps of predetermined lengths along a rectilinear scanning path containing the projection on the surface of the central axis of the sound beam; position signal producing means is adapted to produce digital signals containing information on the position on said surface of the successive points of incidence of the sound beam; ultrasonic equipment is adapted to make said probe emit, on completion of each step of movement, at least one short pulse of ultrasonic energy into the object, and adapted, on receipt of an echo pulse, to produce digital echo signals containing information on the amplitude of said pulse, and on the length of the sound path from said point of incidence to the reflecting point causing the echo pulse; digital computing means is provided, including a first electronic matrix memory for data produced by the examination, said first matrix memory having storage addresses arranged in lines and columns associated with a similar, corresponding network of lines and columns of rectangular co-ordinates in the section plane through the object defined by the scanning path of the ultrasonic probe and the central axis of the sound beam, each storage address being adapted to store data representing said echo amplitudes, and adapted, on receipt of a new data item, to add said new data item to the sum of data items previously stored at said storage address; first control means is provided for storing in said first matrix memory, upon receipt of said position signal and said echo pulse signals, data representing said echo amplitude at all storage addresses located on a circle, having as its centre the storage address associated with said point of incidence, and having as its radius the distance in said first matrix memory corresponding to said length of the sound path through the object; a video screen terminal is provided for controlling the scanning movement of said ultrasonic problem, for controlling the functioning of said ultrasonic equipment, said digital computing means, and said first control means, and for displaying sectional images derived from data stored in said first matrix memory; recording means is provided for producing permanent, electronically readable records of data stored in said first matrix memory, and of sectional images displayed on said screen terminal; and printing means is provided for producing permanent prints of images displayed on said screen terminal.
According to said previous invention, said ultrasonic probe can further be moved over the surface of the object along a number of successive, parallel rectilinear scanning paths at predetermined intervals; said digital computing means then further includes at least one further matrix memory having storage addresses arranged in lines and columns associated with a similar, corresponding network of lines and columns of rectangular co-ordinates in a projection plane parallel to or at right angles to the surface of the object examined, each storage address being adapted to store sums of data items representing said echo amplitudes; further control means is then adapted, on completion of each movement of said ultrasonic probe along the length of a scanning path, to read from the storage addresses of said first matrix memory the highest sums of data items stored in each line or column, to store said highest sums of data items at the corresponding storage addresses in a line or column in said further matrix memory, and to reset all storage addresses in said first matrix memory at zero value; said video screen terminal is then further adapted to control the functioning of said further control means, and to display projection images derived from data stored in said further matrix memory; and said recording means is then further adapted to produce permanent, electronically readable records of data stored in said further matrix memory.
The system according to said previous invention, providing accumulated storage of echo amplitude data values at memory locations corresponding to the actual positions of internal flaws, has in practical examinations led to a drastic increase in the quality and precision of sectional and projection flaw images in comparison with prior art systems, in particular in cases where only one internal flaw has been present in the object examined.
The system has, however, not been entirely satisfactory in cases where a number of internal flaws of different significance have been present in the same sectional plane. The high echo amplitude data values stored in the circular patterns intersecting at the location of a more significant reflector show a tendency to overshadow the lower echo amplitude data values stored at the locations of less significant reflectors, making it difficult or impossible to analyse and evaluate the aggregate flaw images in a correct manner.